Research On Pedestrian Dynamic FFCA Model With Changing Pedestrian Movement Abilities

There are many situations in which a large number of people gathers in a single location.Examples include spectators at music and sports events,commuters in railway and metro stations,and employees in large office buildings.To ensure the safety and comfort of the people present,a careful design of pedestrian facilities and good crowd management are required.Furthermore,in the event of emergencies,such as a fire,a gas leak,or a bomb threat,the efficient evacuation of the facility is of primary importance.In general,in addition to differences in exercise capacity due to age,gender,and baggage,pedestrians may also experience changes in exercise capacity due to physical exertion or environmental changes.The refinement of regional differences in the movement abilities of pedestrians and the investigation of changes in pedestrians’ movement abilities in the evacuation process will be conducive to improving the pedestrians’ access efficiency.In this paper,the main research method is computer simulation.Considering the variation of pedestrians’motion features,the pedestrian flow in channel and room evacuation has been studied to develop effective and optimized evacuation strategies.Modeling pedestrian movement is an interesting problem both in statistical physics and in computational physics.Cellular automata has become the basic model for our simulation research with its high computational efficiency and good flexibility and extendibility.Update schemes of cellular automaton(CA)models for pedestrian dynamics govern the schedule of pedestrian movement.Usually,different update schemes make the models behave in different ways,which should be carefully recalibrated.Thus,in this paper,we investigated the influence of four different update schemes,namely parallel/synchronous scheme,random scheme,order-sequential scheme and shuffled scheme,on pedestrian dynamics.The multi-velocity floor field cellular automaton(FFCA)considering the changes of pedestrians’ moving properties along walking paths and heterogeneity of pedestrians’ walking abilities was used.As for parallel scheme only,the collisions detection and resolution should be considered,resulting in a great difference from any other update schemes.For pedestrian evacuation,the evacuation time is enlarged,and the difference in pedestrians’ walking abilities is better reflected,under parallel scheme.In face of a bottleneck,for example a exit,using a parallel scheme leads to a longer congestion period and a more dispersive density distribution.The exit flow and the space-time distribution of density and velocity have significant discrepancies under four different update schemes when we simulate pedestrian flow with high desired velocity.Update schemes may have no influence on pedestrians in simulation to create tendency to follow others,but sequential and shuffled update scheme may enhance the effect of pedestrians’ familiarity with environments.As a common phenomenon of pedestrian movement,fatigue has a significant negative effect on pedestrian movement,especially when pedestrians move or run with heavy luggage,rescue the wounded in disaster,climb stairs and etc..According to the field observations and previous researches,fatigue coefficient is defined as the decrease of desired velocity in this study.However,previous researches lacked quantitative analysis of the effect of fatigue on pedestrian speed.It has been a great challenge to study the effect of fatigue on pedestrian flow,since pedestrians of heterogeneous walking abilities and the change of pedestrians’ moving properties need to be taken into consideration.Thus,at first,a series of pedestrian experiments,under three different conditions,were conducted to formulate the empirical relationship among fatigue,average free velocity,and walking distance.Then the empirical formulation of pedestrian fatigue was imported into the multi-velocity field floor cellular automata(FFCA)model for following pedestrian dynamics analysis.The velocity ratio was adjusted dynamically to adapt the change of pedestrians’velocity due to fatigue.The fatigue,entrance flow rate and pedestrian’s initial desired velocity are found to have significant effects on the pedestrian flow.The space-time distributions of pedestrian density and velocity were explored in detail,with phase transition analyses from a free flow phase to a congestion phase.Additionally,the"density wave" in the system can be observed if a certain ratio of burdened pedestrians lay in the high density region.The envelope of the "density wave" reaches its maximum amplitude around the entrance position,and gradually diminishes away from the entrance.Multi-directional flow is a typical phenomenon of pedestrian movement ability changing with the evacuation environment.Although people try to avoid pedestrians in different directions in the same channel,bidirectiona flow and vertical crossing flow are still very common,especially at intersections.In experiments and observations,lane formation can be found in multi-directional flow.The effect can beunderstood as a self-organization process,where pedestrians try to minimize the contact with other pedestrians,especially if they have a different desired walking direction.The mechanism which leads to segregation into distinct lanes is not fully understood.Thus,in this paper,we redefined the dynamic floor field,the right priority floor field,and the order parameter for lane formation,and analyzed unidirectional,bidirectional and crossing flow.In this article,the results of simulation are described in several typical fashions,i.e.,the straight channel with periodic/open boundaries,the intersection with open boundaries.Through the analysis of density distribution,fundamental diagram,order parameter and crossing time,we found that the roles of dynamic field and right priority field in different types of flow have similarities and great differences.At the same time,we also explained the generation and maintenance of lane formation under different conditions,and analyzed the transition from local to global congestion.